WinForms重写OnInputLanguageChanging未触发，如何使其生效？

核心原因 #

OnInputLanguageChanging方法仅在当前窗体拥有输入焦点时，输入语言即将变更的场景下才会被触发。如果切换语言时窗体未处于激活状态（无焦点），系统不会向该窗体发送WM_INPUTLANGCHANGING消息，因此方法不会被调用。而OnInputLanguageChanged是语言变更完成后触发，无论窗体是否有焦点，只要语言变更后焦点回到窗体就会触发，所以你能正常看到它工作。

解决方案 #

方案1：确保窗体激活时触发（适用于仅关注窗体活跃场景） #

当你的窗体是活动窗口（拥有输入焦点）时，尝试通过快捷键（如Ctrl+Shift）切换语言，此时OnInputLanguageChanging应该会正常触发。如果仍未触发，检查重写方法中是否调用了基类实现：

protected override void OnInputLanguageChanging(System.Windows.Forms.InputLanguageChangingEventArgs e)
{
    // 在这里添加你的前置处理逻辑，比如取消语言切换
    // e.Cancel = true;
    
    // 必须调用基类方法以保证事件正常传递
    base.OnInputLanguageChanging(e);
}

方案2：全局监听语言切换请求（适用于任何场景） #

如果需要在窗体未激活时也捕获语言切换的前置事件，需要通过Windows API注册全局消息钩子，监听WM_INPUTLANGCHANGING系统消息：

1. 实现全局钩子工具类

using System;
using System.Diagnostics;
using System.Runtime.InteropServices;
using System.Windows.Forms;

public static class InputLanguageGlobalMonitor
{
    private const int WH_GETMESSAGE = 3;
    private const int WM_INPUTLANGCHANGING = 0x0050;
    private const int PM_REMOVE = 1;

    private static IntPtr _hookHandle = IntPtr.Zero;
    private static HookProc _hookCallback;

    public static event EventHandler<InputLanguageChangingEventArgs> InputLanguageChanging;

    public static void StartMonitoring()
    {
        if (_hookHandle != IntPtr.Zero) return;
        
        _hookCallback = HookProc;
        using (var module = Process.GetCurrentProcess().MainModule)
        {
            _hookHandle = SetWindowsHookEx(WH_GETMESSAGE, _hookCallback, GetModuleHandle(module.ModuleName), 0);
        }
    }

    public static void StopMonitoring()
    {
        if (_hookHandle == IntPtr.Zero) return;
        
        UnhookWindowsHookEx(_hookHandle);
        _hookHandle = IntPtr.Zero;
    }

    private static IntPtr HookProc(int nCode, IntPtr wParam, IntPtr lParam)
    {
        if (nCode >= 0 && wParam == (IntPtr)PM_REMOVE)
        {
            var msg = Marshal.PtrToStructure<MSG>(lParam);
            if (msg.message == WM_INPUTLANGCHANGING)
            {
                var culture = new System.Globalization.CultureInfo((int)msg.lParam);
                var inputLang = InputLanguage.FromCulture(culture);
                var args = new InputLanguageChangingEventArgs(inputLang, msg.wParam != IntPtr.Zero);
                
                InputLanguageChanging?.Invoke(null, args);
                
                // 如果需要取消语言切换，返回(IntPtr)1；否则返回CallNextHookEx结果
                if (args.Cancel)
                {
                    return (IntPtr)1;
                }
            }
        }
        return CallNextHookEx(_hookHandle, nCode, wParam, lParam);
    }

    #region P/Invoke 声明
    private delegate IntPtr HookProc(int nCode, IntPtr wParam, IntPtr lParam);

    [DllImport("user32.dll", SetLastError = true)]
    private static extern IntPtr SetWindowsHookEx(int idHook, HookProc lpfn, IntPtr hMod, uint dwThreadId);

    [DllImport("user32.dll")]
    private static extern bool UnhookWindowsHookEx(IntPtr hhk);

    [DllImport("user32.dll")]
    private static extern IntPtr CallNextHookEx(IntPtr hhk, int nCode, IntPtr wParam, IntPtr lParam);

    [DllImport("kernel32.dll")]
    private static extern IntPtr GetModuleHandle(string lpModuleName);

    [StructLayout(LayoutKind.Sequential)]
    private struct MSG
    {
        public IntPtr hwnd;
        public uint message;
        public IntPtr wParam;
        public IntPtr lParam;
        public uint time;
        public POINT pt;
    }

    [StructLayout(LayoutKind.Sequential)]
    private struct POINT
    {
        public int x;
        public int y;
    }
    #endregion
}

2. 在主窗体中使用监听

private void MainForm_Load(object sender, EventArgs e)
{
    InputLanguageGlobalMonitor.StartMonitoring();
    InputLanguageGlobalMonitor.InputLanguageChanging += OnGlobalInputLanguageChanging;
}

protected override void OnFormClosing(FormClosingEventArgs e)
{
    InputLanguageGlobalMonitor.InputLanguageChanging -= OnGlobalInputLanguageChanging;
    InputLanguageGlobalMonitor.StopMonitoring();
    base.OnFormClosing(e);
}

private void OnGlobalInputLanguageChanging(object sender, InputLanguageChangingEventArgs e)
{
    // 在这里处理全局的语言切换前置逻辑
    // 比如取消切换：e.Cancel = true;
}

注意事项 #

• 全局钩子需要程序拥有足够权限，在Windows Vista及以上系统中，可能需要以管理员身份运行程序。
• 若取消语言切换（设置e.Cancel = true），会全局阻止本次语言变更操作，需谨慎使用。

内容的提问来源于stack exchange，提问作者Shark